Flutter ও FastAPI সংযোগ

// lib/core/api/api_client.dart
import 'package:dio/dio.dart';

class ApiClient {
  ApiClient(this._tokens) {
    dio = Dio(BaseOptions(
      baseUrl: const String.fromEnvironment('API_URL', defaultValue: 'http://10.0.2.2:8000'),
      connectTimeout: const Duration(seconds: 10),
      receiveTimeout: const Duration(seconds: 20),
      headers: {'Accept': 'application/json', 'X-App-Version': appVersion},
    ));
    dio.interceptors.add(AuthInterceptor(dio, _tokens));
  }

  final TokenStore _tokens;
  late final Dio dio;
}

import 'package:flutter_secure_storage/flutter_secure_storage.dart';

class TokenStore {
  final _s = const FlutterSecureStorage();
  Future<String?> get access => _s.read(key: 'access');
  Future<String?> get refresh => _s.read(key: 'refresh');
  Future<void> save(String a, String r) async {
    await _s.write(key: 'access', value: a);
    await _s.write(key: 'refresh', value: r);
  }
  Future<void> clear() => _s.deleteAll();
}

class AuthInterceptor extends QueuedInterceptor {     // Queued: একবারে একটা error সামলায়
  AuthInterceptor(this._dio, this._tokens);
  final Dio _dio;
  final TokenStore _tokens;

  @override
  Future<void> onRequest(RequestOptions o, RequestInterceptorHandler h) async {
    final token = await _tokens.access;
    if (token != null) o.headers['Authorization'] = 'Bearer $token';
    h.next(o);
  }

  @override
  Future<void> onError(DioException e, ErrorInterceptorHandler h) async {
    final is401 = e.response?.statusCode == 401;
    final isRefreshCall = e.requestOptions.path.contains('/auth/refresh');
    if (!is401 || isRefreshCall) return h.next(e);

    // অন্য কেউ ইতিমধ্যে refresh করে ফেলেছে? তাহলে নতুন token দিয়ে আবার চেষ্টা
    final current = await _tokens.access;
    final used = (e.requestOptions.headers['Authorization'] as String?)?.replaceFirst('Bearer ', '');
    if (current != null && current != used) {
      return h.resolve(await _retry(e.requestOptions, current));
    }

    try {
      final r = await _dio.post('/v1/auth/refresh', data: {'refresh_token': await _tokens.refresh});
      await _tokens.save(r.data['access_token'], r.data['refresh_token']);
      h.resolve(await _retry(e.requestOptions, r.data['access_token']));
    } catch (_) {
      await _tokens.clear();
      authEvents.add(AuthEvent.loggedOut);          // login screen এ পাঠাও
      h.next(e);
    }
  }

  Future<Response> _retry(RequestOptions o, String token) {
    o.headers['Authorization'] = 'Bearer $token';
    return _dio.fetch(o);
  }
}

sealed class AppFailure {
  const AppFailure(this.message);
  final String message;
}
class NetworkFailure extends AppFailure { const NetworkFailure() : super('Internet সংযোগ নেই'); }
class ValidationFailure extends AppFailure {
  const ValidationFailure(super.message, this.fields);
  final Map<String, String> fields;
}
class ServerFailure extends AppFailure {
  const ServerFailure(super.message, this.code, this.requestId);
  final String code;
  final String? requestId;          // support এ দেখানোর জন্য
}

AppFailure mapError(DioException e) {
  if (e.type == DioExceptionType.connectionError || e.type == DioExceptionType.connectionTimeout) {
    return const NetworkFailure();
  }
  final err = (e.response?.data as Map?)?['error'] as Map?;
  final rid = e.response?.headers.value('x-request-id');
  if (e.response?.statusCode == 422) {
    return ValidationFailure(err?['message'] ?? 'তথ্য ঠিক নেই',
        Map<String, String>.from(err?['fields'] ?? {}));
  }
  return ServerFailure(err?['message'] ?? 'সমস্যা হয়েছে', err?['code'] ?? 'UNKNOWN', rid);
}

final token = await FirebaseMessaging.instance.getToken();
await api.dio.post('/v1/devices', data: {'fcm_token': token, 'platform': Platform.operatingSystem});
FirebaseMessaging.instance.onTokenRefresh.listen((t) => api.dio.post('/v1/devices', data: {'fcm_token': t}));

uv add firebase-admin

# workers/push.py
import firebase_admin
from firebase_admin import credentials, messaging

firebase_admin.initialize_app(credentials.Certificate(settings.firebase_credentials_path))


@celery.task(autoretry_for=(Exception,), retry_backoff=True, max_retries=5)
def push_to_user(user_id: int, title: str, body: str, data: dict[str, str]) -> None:
    tokens = get_device_tokens(user_id)
    if not tokens:
        return
    resp = messaging.send_each_for_multicast(messaging.MulticastMessage(
        tokens=tokens,
        notification=messaging.Notification(title=title, body=body),
        data=data,                                     # app খুললে কোন screen এ যাবে
        android=messaging.AndroidConfig(priority="high"),
    ))
    for token, r in zip(tokens, resp.responses):
        if not r.success and isinstance(r.exception, messaging.UnregisteredError):
            remove_device_token(token)                 # app uninstall হয়েছে, token বাদ